quench and compression ratio Help!

[Tedo44YJ]

just slapped my 4.2 crank in today with the 4.0 rods and kb ic944-040's
with the compression ratio calculator i got a 9.25 SCR, 6.82 DCR, and a .070 Quench

if i shave .020 of the block it says i will get a 9.61 ScR, 7.07 DCR and .050 Quench

is .070 too much for quench? or should i get the block decked and go with the higher SCR of 9.61? is that CR too much? what octane do i run? ive been racking my brain on this all day and need to know if i should take it back to the machine shop. Thanks!

[Cheromaniac]

is .070 too much for quench? or should i get the block decked and go with the higher SCR of 9.61?

Your maths are correct and yes, 0.070" is higher than ideal for proper quench action in the combustion chambers so have the block decked 0.020".

[Russ Pottenger]

Another suggestion assuming you're not finished with your cylinder head yet.

Using your numbers, surfacing the block an additional .010 for a total of .030 would bring your quench to a more desirable .040
That should change your static from 9.61 to something like 9.81 If you lose 2cc in your chamber you'll be back to your 9.61 You can achieve that by either doing some chamber work in your cylinder head, or the easiest would be to upgrade to a Chevy LS 1 valve. The Manley stainless steel valves I use in my heads have somewhat of a tulip head design that has a 2cc cup in in the head of the exhaust valve. They do this for increased airflow.
It's another good side benefit in utilizing them in the Jeep heads

If you're interested i'd be happy to set you up with a complete valvetrain kit.

Russ

[Tedo44YJ]

Your maths are correct and yes, 0.070" is higher than ideal for proper quench action in the combustion chambers so have the block decked 0.020".

Ok that's what i thought. Is 9.6:1 SCR pretty high for a cast iron head? Can I still run pump gas? I don't mind having to run 91 octane just as long as it's available at a pump.

[Russ Pottenger]

Your maths are correct and yes, 0.070" is higher than ideal for proper quench action in the combustion chambers so have the block decked 0.020".

Ok that's what i thought. Is 9.6:1 SCR pretty high for a cast iron head? Can I still run pump gas? I don't mind having to run 91 octane just as long as it's available at a pump.

With a tight quench yes.
.050 and beyond probably not.
We haven't discussed or factored in the camshaft and its affect on cylinder pressure.

Bottom line is the closer you get to .035 you'll be rewarded. At .070 you essentially have lost or don't have a quench.

[Tedo44YJ]

If you're interested i'd be happy to set you up with a complete valvetrain kit.

Russ

That's a good idea, I do have my head done already but new valves wouldn't be too hard or expensive to get done right?

[Tedo44YJ]

Also, I'm running a stock cam for the 95 block. Heard too many horror stories about the aftermarket cams and decided to keep it stock

[Russ Pottenger]

If you're interested i'd be happy to set you up with a complete valvetrain kit.

Russ

That's a good idea, I do have my head done already but new valves wouldn't be too hard or expensive to get done right?

Unfortunately doing the Chevrolet LS 1 valvetrain upgrade requires valve guide honing and valveseat work because of the larger valve head diameters. To receive the full benefit of the larger valve, pocket porting is highly recommended.

[Tedo44YJ]

Ok so I think I'm going to go with shaving .020" of the block and running with the .050" quench and 9.61 CR. I'll run 91 octane and if I get any pinging I'll see what I can do about some head work? Maybe a thinner head gasket?